Mufflers for internal combustion engines

ABSTRACT

An exhaust muffler of compact form for use on small two-stroke internal combustion engines, and comprising a housing having an inlet and an outlet for exhaust gases and defining an indirect passage therethrough between the inlet and outlet for the exhaust gases. A wad of sound absorbing material is positioned in a part of the housing not traversed by the exhaust gases and receives the shock wave component of the exhaust gases by reflection from a plate located opposite the inlet.

United States Patent Snodgrass et al.

151 3,685,613 [451 Aug. 22, 1972 MUFFLERS FOR INTERNAL COMBUSTIONENGINES [72] Inventors: Kenneth William Snorlgrass; William HenrySteele; Alan Wilson; Ross Leslie Phelps, all of Milperra,

New South Wales, Australia [73] Assignee: Victa Limited, Milperra, NewSouth Wales, Australia [22] Filed: May 11, 1971 21 Appl. No.: 142,249

[30] Foreign Application Priority Data May 12, 1970 Australia ..PA 1183[52] U.S. Cl ..181/33K, 181/50, 181/53, 181/40 [51] Int. Cl. ..F01nl/10, F01n 7/18 [58] Field of Search ..181/33 K, 47 B, 40, 42, 50,181/53, 36 R, 61, 35 C, 33 E [56] References Cited UNITED STATES PATENTS3,204,619 9/1965 Rubinowitz et al ..181/40 2,501,306 3/1950 Bessiere..181/42 3,168,936 2/ 1965 Gordon ..181/40 3,378,099 4/1968 Gordon181/40 3,404,749 10/ 1968 Miller et al. ..181/40 3,530,840 9/1970 Freyn"181/33 K FOREIGN PATENTS OR APPLICATIONS 610,841 -l0/ 1948 GreatBritain ..181/42 483,566 8/1953 Italy ..181/40 1,157,103 12/1957 France..181/40 746,590 3/1956 Great Britain ..181/33 K Primary Examiner-RobertS. Ward, Jr. Attorney-Waters, Roditi, Schwartz & Nissen [57] ABSTRACT Anexhaust muffler of compact form for use on small two-stroke internalcombustion engines, and comprising a housing having an inlet and anoutlet for exhaust gases and defining an indirect passage therethroughbetween the inlet and outlet for the exhaust gases. A wad of soundabsorbing material is positioned in a part of the housing not traversedby the exhaust gases and receives the shock wave component of theexhaust gases by reflection from a plate located opposite the inlet.

7 Claims, 4 Drawing Figures MUFFLERS FOR INTERNAL COMBUSTION ENGINESThis invention relates to engine mufflers and more particularly tomufflers for small two stroke internal combustion engines used as primemovers for lawn mowers or other small appliances.

In this application of exhaust mufflers an inexpensive, compact unit isrequired and for these reasons such mufflers have been constructed toprovide tortuous passages for the exhaust gases. Generally thesepassages attenuate the pressure front component of the exhaust gases andcreate a back-pressure, and do not efficiently attenuate the shock wavecomponent. Attempts have been made to replace the tortuous passages inthe muffler by sound absorbing wads in the through path of the exhaustgases. However, when applied to small engines, such as two strokeengines, these wads become clogged with oil and other matter and,although continuing to absorb sound, they excessively impede the passageof exhaust gases.

One object of the invention is to provide an exhaust muffler for aninternal combustion engine which is efficient and durable and of compactconstruction.

Other objects are to provide an exhaust muffler which is relativelyinexpensive to produce, acceptably leakproof, and readily detachablefrom an associated engine.

A preferred form of the invention will now be described with referenceto the accompanying drawings, in which:

FIG. 1 is an exploded perspective view of the component parts of amuffler constructed in accordance with the invention;

FIG. 2 is a perspective view of the assembled muffler with a portionpartly cut away to show the gas and sound energy flow through theinterior;

FIG. 3 is a fragmentary perspective view showing the peripheral edges ofthe back plate, separator plate and cover before the seaming operationhas been carried out to secure them together; and,

FIG. 4 is an elevation of the muffler, in section through its inletport; shown secured to the exhaust port of a typical engine.

With reference particularly to FIG. 1, a back plate 5 of the muffler isa pressing of metal with an upturned flange 6 and a land 7 formed aboutits periphery. A main wall 8 of the plate 5 is press-formed below thelevel of the land 7 to form a well 9. An inlet port 10 is formed in thewell 9 with the circumference of said port dished to form a seating fora sealing gasket 11 (see FIGS. 2 and 4).

The land 7 in the back plate 5 is extended at one corner 7A to form anouter edge 12 from which the up turned flange 6 is omitted. A secondarywell 13, shallower than the well 9, is formed at the corner 7A toconstitute a discharge port 14 of the muffler.

The land 7 is also extended inwardly at 713, to approximately thelongitudinal center line of the plate 5, to form a partition between thewells 9 and 13. An integral junction wall 15 between said wells isangled approximately diagonally with respect to the general rectangularconfiguration of the back plate 5.

A separator plate 16 is adapted to seat upon the land 7 of the backplate 5 with its peripheral edge 17 within the flange 6. The saidperipheral edge 17 is extended at 17A so as to correspond to'theextension 7A in the back plate 5. The edge 17A spaced away from the well13, completes the configuration of the exhaust port 14. An inwardlypressed aperture 18 is formed in the plate 16 so that the edge of saidaperture engages the inner face of the dished inlet port 10. Diagonallydisposed stiffening ribs 19 are pressed into the surface of the plate 16to one side of the aperture 18. Three holes 20 are formed to the otherside of said aperture 18.

A reflector plate 21 is secured to the plate 16 in line with the port18. The plate 21 is approximately V- shaped with one wall 22 at rightangles to the plate 16. The wall 22 is perforated over its whole surfacewith a series of holes 23 (FIG. 2). The other wall 24 is angularlydisposed to the plate 16 and three holes 25 are formed near theconjunctional apex 26 of the two walls 22 and 24. The lower edges of thewalls 22 and 24 are outwardly flanged as at 27 and said flanges 27 arespot welded to the plate 16.

A wad 28 of sound absorbing glass fibers, or other suitable material, ispositioned on the plate 16, adjacent the wall 22 of the reflector plate21. A deeply dished cover 29 is provided to enclose the wad 28 and plate21. An outwardly turned flange 30 is formed marginally about the cover29.

It will be seen that the marginal edge 17 of the plate 16 is setangularly away from the plane of said plate 16 c maintained even thoughthe curl relaxes a little after removal from the press. The form 31 inthe separator plate 16 being reduced by the seaming blow, contributes aspring-back force acting to maintain an interference condition in theseam. This spring-back can be arranged to more than compensate for therelaxation in the curled flange 6. This arrangement thus ensures thatoil leakage from the muffler is reduced to a minimum.

In FIG. 4 the muffler is shown secured to the exhaust port 32 of atypical internal combustion engine cylinder 33. Spring clips 33A areadapted to snap over the curled flange 6 to hold the muffler in place.In addition a bracket 34, extending from the cover 29 can be bolted toan upper cover 35 of the engine.

The paths of the gases and their sound energy component are shown inFIG. 2 and it will be seen that the wad 28 is laterally disposed withrespect to the passage through the muffler for exhaust gases. The gases36 and sound energy waves 36A pass through the ports 10 and 18 andstrike the inclined wall 24 of the reflector plate 21. The sound energywaves 36A are reflected through the holes 23 in the wall 22 and areabsorbed within the fiber wad 28. The gases 36 pass up into the apex 26of the plate 21 and emerge through the holes 25. They then pass throughthe holes 20 in the plate 16 and travel between said plate and the well9 in the back plate 5. They are then turned into the well 13 and emergedownwardly through the exhaust port 14 which passes through a passage37A in the baseplate 37 of a lawn mower or other appliance driven by theengine and to which the engine cylinder 33 is mounted.

The back pressure is therefore not determined by the gas flow impedancein the sound absorbing section, nor by the state of clogging existing inthe wad 28. The back pressure depends upon the impedance to flow in theflow channels, which can be left fairly open.

For use on rotary lawn mowers, the discharge may be beneath thebaseplate 37, exploiting the additional sound attenuation possible byavoiding discharge directly into the atmosphere. The grass surface andthe cuttings stream are helpful in this regard, being somewhat soundabsorbent.

The ribs 19 in the plate 16, and also a dimple 38 in the back plate 5adjacent the exhaust port 14 prevent resonant vibrations being set up inthese metallic members and thus limit the transmission of sound energytherefrom.

From the above description it will be seen that in its most general formthe invention provides an exhaust muffler for an internal combustionengine comprising a housing having an inlet and an outlet for gasesexhausted from an exhaust port of the engine, means for attaching themuffler housing to the engine with said inlet in communication with saidexhaust port, means within said housing for defining an indirect passagefor exhaust gases between said inlet and said outlet, and a wad of soundabsorbing material exposed to the exhaust gases and laterally disposedwith respect to at least part of said passage.

A single embodiment has been described in the above passages but it isto be understood that other forms are possible within the scope of theinvention.

What we claim is:

1. An exhaust muffler for an internal combustion engine comprising ahousing including a dished'outer shell, an outer back plate and aninternal separator plate substantially parallel with the back plate toform with said back plate an exhausting chamber and with said outershell a muffler chamber, a wad of sound absorbing material in one partof the muffler chamber, a perforated sound reflector plate opposite tothe wad in another part of the muffler chamber, an inlet and an outletin the housing for gases exhausted from an exhaust port of the engine,said inlet being sealed from said exhausting chamber and passing throughsaid back plate and said separator plate into said other part of themuffler chamber to direct exhaust gases onto and through said soundreflector plate, said outlet being connected with said exhaustingchamber, and means for attaching the muffler housing to the engine withsaid inlet in communication with said exhaust port.

2. An exhaust muffler as claimed in claim 1, wherein reinforcing ribsare fonned in the separator plate to resist vibration of said plate whenin use.

3. An exhaust muffler for an internal combustion engine provided with anexhaust port, comprising a housing including a dished outer shell, anouter back plate closing an open side of the shell, an internalpartitioning separator plate defining together with the back plate anexhausting chamber and together with the outer shell a muffler chamber,a perforated panel between the separator plate and the shell dividingthe muffler chamber into two compartments, a wad of sound absorbingmaterial in a first one of said compartments, an inlet for exhaust gasessealed from the exha s tin ch her and s' throu an int rnai eparator gateiflto a s cond one 0 said compartments, a reflector plate in the secondcompartment dividing same into two parts and having an inclined surfacein a first of said compartment parts and opposite the inlet to reflectthe shock wave component of exhaust gases entering the inlet towards thesound absorbing wad, means for permitting passage of exhaust gases fromthe inlet through the first part of the second compartment into a secondof the said parts thereof and thence into'the exhausting chamber, and anoutlet for exhaust gases connected with the exhausting chamber.

4. An exhaust muffler as claimed in claim 3, wherein a peripheralmarginal edge area of said outer shell, back plate and separator plateare clamped together in a peripheral folded joint.

5. An exhaust muffler as claimed in claim 4, wherein the marginal edgearea of said back plate is folded around the marginal edge areas of theseparator plate and the outer shell, and the marginal edge area of theseparator plate is set angularly away from the plane of said separatorplate to effect an interference condition in the resulting seam.

6. An exhaust muffler as claimed in claim 3, wherein. the muffler isgenerally rectangular and said outlet is located near one end of themuffler and directed in a direction substantially normal to that atwhich the inlet is directed.

7. An exhaust muffler as claimed in claim 3, wherein the inlet is anaperture in an annular dished seat for an annular sealing gasket adaptedto accept an exhaust port spigot from the engine, said mufflercomprising spring clips for holding the housing to the engine with thespigot forced onto the sealing gasket on the seat.

the back plate

1. An exhaust muffler for an internal combustion engine comprising ahousing including a dished outer shell, an outer back plate and aninternal separator plate substantially parallel with the back plate toform with said back plate an exhausting chamber and with said outershell a muffler chamber, a wad of sound absorbing material in one partof the muffler chamber, a perforated sound reflector plate opposite tothe wad in another part of the muffler chamber, an inlet and an outletin the housing for gases exhausted from an exhaust port of the engine,said inlet being sealed from said exhausting chamber and passing throughsaid back plate and said separator plate into said other part of themuffler chamber to direct exhaust gases onto and through said soundreflector plate, said outlet being connected with said exhaustingchamber, and means for attaching the muffler housing to the engine withsaid inlet in communication with said exhaust port.
 2. An exhaustmuffler as claimed in claim 1, wherein reinforcing ribs are formed inthe separator plate to resist vibration of said plate when in use.
 3. Anexhaust muffler for an internal combustion engine provided with anexhaust port, comprising a housing including a dished outer shell, anouter back plate closing an open side of the shell, an internalpartitioning separator plate defining together with the back plate anexhausting chamber and together with the outer shell a muffler chamber,a perforated panel between the separator plate and the shell dividingthe muffler chamber into two compartments, a wad of sound absorbingmaterial in a first one of said compartments, an inlet for exhaust gasessealed from the exhausting chamber and passing through the back plateand internal separator plate into a second one of said compartments, areflector plate in the second compartment dividing same into two partsand having an inclined surface in a first of said compartment parts andopposite the inlet to reflect the shock wave component of exhaust gasesentering the inlet towards the sound absorbing wad, means for permittingpassage of exhaust gases from the inlet through the first part of thesecond compartment into a second of the said parts thereof and thenceinto the exhausting chamber, and an outlet for exhaust gases connectedwith the exhausting chamber.
 4. An exhaust muffler as claimed in clAim3, wherein a peripheral marginal edge area of said outer shell, backplate and separator plate are clamped together in a peripheral foldedjoint.
 5. An exhaust muffler as claimed in claim 4, wherein the marginaledge area of said back plate is folded around the marginal edge areas ofthe separator plate and the outer shell, and the marginal edge area ofthe separator plate is set angularly away from the plane of saidseparator plate to effect an interference condition in the resultingseam.
 6. An exhaust muffler as claimed in claim 3, wherein the muffleris generally rectangular and said outlet is located near one end of themuffler and directed in a direction substantially normal to that atwhich the inlet is directed.
 7. An exhaust muffler as claimed in claim3, wherein the inlet is an aperture in an annular dished seat for anannular sealing gasket adapted to accept an exhaust port spigot from theengine, said muffler comprising spring clips for holding the housing tothe engine with the spigot forced onto the sealing gasket on the seat.